xconnect pw between IOS XR & IOS XE

[Julie Tupling]

We have a small Service provider network with a combination of ASR 9006 and ASR 920 routers.  We have MPLS configured on the backbone network.  We have a customer that has an external Ethernet circuit from London that is connected to a port on the ASR 9006 - they want to use this circuit to transport 2 VLANS into our network.  One VLAN (VLAN 100) will go to an ASR 920 at location A and the other VLAN (VLAN 200) will go to an ASR 920 router at location B. At each location (A & B). I've uploaded a simplified drawing showing the pertinent routers and layout.

If we were going between 2 ASR 920s, I think it would be pretty easy, you can add multiple service instances to an interface. but since the interface that the external customer circuit connects to is on an ASR 9006 (IOS XR) I'm not sure how to configure the xconnect between the ASR 9006 and the ASR 920 routers. How do I get the ASR 9006 to support 2 VLANS and distribute them to the ASR 920s? 

Thanks in advance for any help - it is hard to find examples of configurations where there is a combination of IOS XR and IOS XE routers....

[Olev Vallaste]

I think you need to configure Bridge Group and Bridge-domains in that BG. And then stitching in this BDs xconnectx and dot1q subinterfaces. Or you can use local xconnect between PW and dot1q-subinterface.

For example:

ASR 9006
=========

method 1. local xconnect in the PW-group
------------------------
interface Gi 0/1/0/1.100 l2transport
 description CUST1-VLAN-100
 encapsulation dot1q 100
 rewrite ingress tag pop 1 symmetric

interface Gi 0/1/0/1.200 l2transport
 description CUST1-VLAN-200
 encapsulation dot1q 200
 rewrite ingress tag pop 1 symmetric
!
l2vpn
!
 xconnect group CUST1
  p2p CUST1-VLAN-100
   interface Gi 0/1/0/1.100
   neighbor ipv4 <loopback ip-address ASR920 Location A> pw-id 100 (or those pw-id that used)
   !
  p2p CUST1-VLAN-200
   interface Gi 0/1/0/1.200
   neighbor ipv4 <loopback ip-address ASR920 Location B> pw-id 200 (or those pw-id that used)

Method 2. Bridge-group and Bridge-domains
interface Gi 0/1/0/1.100 l2transport
 description CUST1-VLAN-100
 encapsulation dot1q 100
 rewrite ingress tag pop 1 symmetric

interface Gi 0/1/0/1.200 l2transport
 description CUST1-VLAN-200
 encapsulation dot1q 200
 rewrite ingress tag pop 1 symmetric

l2vpn
! 
 bridge group CUST1
  !
  bridge-domain CUST1-VLAN-100
    mtu 1600
    interface Gi 0/1/0/1.100
    !
    neighbor <loopback ip-address ASR920 Location A> pw-id 100 (or those pw-id that used)

  bridge-domain CUST1-VLAN-200
    mtu 1600
    interface Gi 0/1/0/1.200
    !
    neighbor <loopback ip-address ASR920 Location B> pw-id 200 (or those pw-id that used)

Config with BG and BDs is more preferred, if you for example use BGP autodiscovery for loopback addresses for targeted-ldp sessions buliding between PEs.

[Olev Vallaste]

And addition.

Here is the great document about L2VPN  on IOS XR

http://www.cisco.com/c/en/us/support/docs/routers/asr-9000-series-aggregation-services-routers/116453-technote-ios-xr-l2vpn-00.html

[Julie Tupling]

Olev,

Thank you... I have another question though:  I thought if you were only doing point-to-point circuits (E-LINE) it was better to use xconnect.  That BG & BD were for VPLS circuits - is that incorrect?  These circuits will only be point-to-point.

Do you know how the ASR920s should be configured to support this - I know how to do the BG/BD config on the ASR920 routers but since that supports MAC address learning, which isn't needed in this case, I thought it would be better to configure the circuits as xconnects.

[Olev Vallaste]

Julie,

What should be better - ptp xconnect or BG and BD - its depends of your target scheme.

If you need only ptp sconnects, without MAC learning and maintaining MAC address tables, so - yes, ptp xconnects are better.

I think config for ASR920 in Location A and Location B will be something like that:

Location A
ASR920
===============

for tagged interface and pw-id 100
--------------------------------------------------
interface Gi 0/0/1
 service instance 100 ethernet
  description CUST1-VLAN-100
  encapsulation dot1q 100
  rewrite ingress tag pop 1 symmetric
  xconnect <ASR 9006 Loopback ip addr> 100 encapsulation mpls
   mtu 1600


for untagged interface and pw-id 100
--------------------------------------------------
interface Gi 0/0/1
 service instance 100 ethernet
 description CUST1-VLAN-100
  encapsulation untagged
  xconnect <ASR 9006 Loopback ip addr> 100 encapsulation mpls
   mtu 1600

Location B
ASR920
===============

for tagged interface and pw-id 200
--------------------------------------------------
interface Gi 0/0/3
 service instance 200 ethernet
  description CUST1-VLAN-200
  encapsulation dot1q 200
  rewrite ingress tag pop 1 symmetric
  xconnect <ASR 9006 Loopback ip addr> 200 encapsulation mpls
   mtu 1600


for untagged interface and pw-id 200
--------------------------------------------------
interface Gi 0/0/3
 service instance 200 ethernet
  description CUST1-VLAN-200
  encapsulation untagged
  xconnect <ASR 9006 Loopback ip addr> 200 encapsulation mpls
   mtu 1600

May be you dont need to change the MTU - so these strings are useless (on both sides^ ASR920 and ASR9006.

On the ASR9006 side you can choose from both previously described variants. It is working in both cases, as I remember...